1. Field of the Invention
The present invention relates to an operating machine such as a mobile crane or a shovel, and more particularly to an operating machine equipped with two batteries for performing idling stop control.
2. Background Art
Various proposals have been made recently for improving fuel efficiency, reducing exhaust gas and noise, and so on in an operating machine such as a mobile crane or a shovel by equipping the operating machine with an engine control device that performs idling stop control, in which an engine is stopped automatically during an idling operation, when a predetermined condition is established. Japanese Patent Application Publication No. 2006-62782, for example, describes an engine control device which, during a load lifting operation by a mobile crane, automatically stops an engine when a condition in which a crane operation is not underway and a condition in which a suspended load does not exist remain established simultaneously and continuously for a predetermined time, taking into consideration a situation in which an operator waits inside a cab between operations and so on.
Incidentally, a compressor of an air-conditioning device provided to condition air in the cab of the operating machine is typically driven by power from the engine either directly or via oil pressure, and cannot therefore be used when the engine is stopped. However, it is desirable for the operator to be able to use the air-conditioning device while waiting in the cab even during an idling stop in the engine. To realize this, structural improvements such as modifications must be implemented on the operating machine so that the compressor of the air-conditioning device can be driven by an electric motor, and the operating machine must be equipped with a second battery used to drive a load of an electric component such as the electric motor for driving the compressor during an idling stop in addition to a first battery provided normally to start the engine. As shown in FIG. 18, a circuit configuration in which an electric component load b, a first battery c, and a second battery d provided in the operating machine are connected in parallel to a power generation device a such as an alternator that is driven by the engine and a switch (not shown) or the like is used to enable discharging (energization) from the first battery c or the second battery d to the electric component load b side and charging from the power generation device a to the first battery c and the second battery d may be employed as a circuit configuration in this case.
With this circuit configuration, however, even when the first battery c and the second battery d are identical in type and capacity, if an engine rotation speed is low during charging from the power generation device a to the first battery c and the second battery d such that a sufficient power generation current cannot be secured in the power generation device a, charging/discharging occurs between the two batteries c, d in accordance with a capacity difference (more specifically, a residual capacity difference) between the two batteries c, d. In particular, the second battery d used to drive the electric component load b during an idling stop performs deeper discharging than the first battery c, and therefore discharging occurs from the first battery c to the second battery d. Here, when a degree of discharge of the second battery d is excessive, a discharge amount from the first battery c increases during charging. If, in this case, a sufficient charging time cannot be secured due to interruption of an operation by the operating machine or the like, the residual capacity of the first battery c does not satisfy a capacity required to start the engine, and as a result, an engine startup fault occurs during a subsequent engine startup operation.